Support Apple clang specific compilation/linking flags to enable OpenMP

extension_helpers/_openmp_helpers.py

@@ -19,10 +19,11 @@
 import datetime
 import tempfile
 import subprocess
+import textwrap
 
 from setuptools.command.build_ext import customize_compiler, get_config_var, new_compiler
 
-from ._setup_helpers import get_compiler
+from ._setup_helpers import check_apple_clang, get_compiler
 
 __all__ = ['add_openmp_flags_if_available']
 
@@ -134,8 +135,41 @@ def get_openmp_flags():
             link_flags.append('-L' + lib_path)
             link_flags.append('-Wl,-rpath,' + lib_path)
 
-        compile_flags.append('-fopenmp')
-        link_flags.append('-fopenmp')
+        if not check_apple_clang():
+            compile_flags.append('-fopenmp')
+            link_flags.append('-fopenmp')
+        else:
+            msg = textwrap.dedent(
+                """\
+                You are using Apple Clang compiler.
+
+                Your system should be prepared:
+                1. You should have specfically installed OpenMP,
+                   for instance by running `brew install libomp`.
+                2. OpenMP source and library should be findable by the compiler.
+
+                By default, OpenMP source and library will be looked in
+                `/usr/local/opt/libomp/include` and `/usr/local/opt/libomp/lib`
+                respectively.
+
+                To use specific OpenMP source and library paths, you can setup
+                the following environment variables `CFLAGS` and `LDFLAGS`
+                before any compilation/installation, e.g.
+                ```
+                export CFLAGS="-I/usr/local/opt/libomp/include"
+                export LDFLAGS="-L/usr/local/opt/libomp/lib"
+                ```
+                """
+            )
+            log.warn(msg)
+            compile_flags.append('-Xpreprocessor -fopenmp')
+            if not 'CFLAG' in os.environ and \
+                os.path.isdir('/usr/local/opt/libomp/include'):
+                compile_flags.append('-I/usr/local/opt/libomp/include')
+            link_flags.append('-lomp')
+            if not 'LDFLAG' in os.environ and \
+                os.path.isdir('/usr/local/opt/libomp/lib'):
+                link_flags.append('-L/usr/local/opt/libomp/lib')
 
     return {'compiler_flags': compile_flags, 'linker_flags': link_flags}
 
@@ -189,12 +223,12 @@ def check_openmp_support(openmp_flags=None):
 
             # Compile, test program
             ccompiler.compile(['test_openmp.c'], output_dir='objects',
-                              extra_postargs=compile_flags)
+                              extra_preargs=compile_flags)
 
             # Link test program
             objects = glob.glob(os.path.join('objects', '*' + ccompiler.obj_extension))
             ccompiler.link_executable(objects, 'test_openmp',
-                                      extra_postargs=link_flags)
+                                      extra_preargs=link_flags)
 
             # Run test program
             output = subprocess.check_output('./test_openmp')

extension_helpers/_setup_helpers.py

@@ -12,7 +12,7 @@
 from collections import defaultdict
 
 from setuptools import Extension, find_packages
-from setuptools.command.build_ext import new_compiler
+from setuptools.command.build_ext import customize_compiler,new_compiler
 
 from ._utils import import_file, walk_skip_hidden
 
@@ -36,6 +36,32 @@ def get_compiler():
     return new_compiler().compiler_type
 
 
+def check_apple_clang():
+    """
+    Detemines if compiler that will be used to build extension modules is
+    'Apple Clang' (which requires a specific management of OpenMP compilation
+    and linking flags).
+
+    In addition, it may require that you install `libomp` (e.g. with
+    `brew install libomp`).
+
+    Returns
+    -------
+    apple_clang : bool
+        Indicator whether current compiler is 'Apple Clang'.
+    """
+    try:
+        ccompiler = new_compiler()
+        customize_compiler(ccompiler)
+        compiler_version = subprocess.run(
+            [ccompiler.compiler[0], "--version"], capture_output=True
+        )
+        apple_clang = "Apple clang" in str(compiler_version.stdout)
+    except Exception:
+        apple_clang = False
+    return apple_clang
+
+
 def get_extensions(srcdir='.'):
     """
     Collect all extensions from Cython files and ``setup_package.py`` files.

extension_helpers/tests/test_setup_helpers.py

@@ -7,7 +7,7 @@
 
 import pytest
 
-from .._setup_helpers import get_compiler, get_extensions
+from .._setup_helpers import check_apple_clang, get_compiler, get_extensions
 from . import cleanup_import, run_setup
 
 extension_helpers_PATH = os.path.abspath(os.path.join(os.path.dirname(__file__), '..', '..'))  # noqa
@@ -27,6 +27,9 @@ def teardown_module(module):
 def test_get_compiler():
     assert get_compiler() in POSSIBLE_COMPILERS
 
+def test_check_apple_clang():
+    assert check_apple_clang() in [True, False]
+
 
 def _extension_test_package(tmpdir, request, extension_type='c',
                             include_numpy=False):